#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>

int main()
{
	int sum(int x);
	int n; 
	scanf("%d", &n);
	printf("%d", sum(n));
	return 0;
}
int sum(int x)
{
	int y = 0;
	for (int i = 1; i <= x; i++) {
		y += i;
	}
	return(y);
}